Piezoelectric/electrostrictive element

ABSTRACT

In the manufacture of a laminated piezoelectric/electrostrictive element by lamination of a piezoelectric/electrostrictive film and an electrode film containing either platinum or an alloy composed mainly of platinum and having a thickness of 2.0 μm or less, both or either one of yttrium oxide (Y 2 O 3 ) and cerium oxide (CeO 2 ) is added to the electrode film or the piezoelectric/electrostrictive film, and the electrode film and the piezoelectric/electrostrictive film are fired simultaneously. This simultaneously achieves a reduced thickness and improved thermal resistance of the electrode film and a reduced change in piezoelectric/electrostrictive properties with time, thereby producing a piezoelectric/electrostrictive element with good initial piezoelectric/electrostrictive properties and with a small change in the piezoelectric/electrostrictive properties with time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/032,128, filed Feb. 15, 2008, which claims the benefit ofU.S. patent application Ser. No. 60/890,636, filed Feb. 20, 2007, theentireties of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laminatedpiezoelectric/electrostrictive element.

2. Description of the Related Art

In a laminated piezoelectric/electrostrictive element formed bylaminating a piezoelectric/electrostrictive film and an electrode film,for sufficient densification of the piezoelectric/electrostrictive film,it is necessary to fire the piezoelectric/electrostrictive film at atemperature of 1200° C. or higher. For this reason, the electrode filmthat is fired simultaneously with the piezoelectric/electrostrictivefilm needs to have thermal resistance capable of withstandingtemperatures of 1200° C. or higher. Thus, platinum that may contributeto an improvement in the thermal resistance of the electrode film isoften selected as a material for the electrode film fired simultaneouslywith the piezoelectric/electrostrictive film.

Meanwhile, in order to improve the piezoelectric/electrostrictiveproperties of the laminated piezoelectric/electrostrictive element,reducing the thickness of the electrode film as an inner-layer electrodeis effective.

In conventional techniques, a platinum powder contained in an electrodepaste used for formation of the electrode film is pulverized into smallparticles to reduce the thickness of the electrode film, and a varietyof oxides are added to the platinum powder in order to improve thethermal resistance of the electrode film. However, those conventionaltechniques have the problem that reducing the thickness of the electrodefilm to 2.0 μm or less reduces the thermal resistance of the electrodefilm, thereby causing disconnection of the electrode film at the time ofsimultaneous firing.

One solution that has been suggested to address this problem is to, inaddition to adding a variety of oxides to a platinum powder, control thecrystallite diameter of the platinum powder to be within the range of 60nm to 100 nm through thermal treatment, thereby to improve the thermalresistance of the electrode film (Japanese Patent Application Laid-OpenNos. 2006-302848 and 2006-299385).

This solution results in a reduced thickness and improved thermalresistance of the electrode film, but there is still a problem with thepiezoelectric/electrostrictive properties greatly changing with time.

SUMMARY OF THE INVENTION

The invention relates to a laminated piezoelectric/electrostrictiveelement. According to a first aspect of the invention, a laminatedpiezoelectric/electrostrictive element includes the follows: anelectrode film being a sintered body of either platinum or an alloycomposed mainly of platinum and having a thickness of 2.0 μm or less;and a piezoelectric/electrostrictive film being a sintered body of apiezoelectric/electrostrictive material containing 0.01 to 0.60 part byweight of yttrium oxide to 100 parts by weight of platinum contained inthe electrode film and containing 0.1 to less than 1.8 parts by weightof cerium oxide to 1 part by weight of yttrium oxide.

According to a second aspect of the invention, a laminatedpiezoelectric/electrostrictive element is manufactured by the followingsteps: the step of forming a piezoelectric/electrostrictive filmincluding a piezoelectric/electrostrictive material; the step of formingan electrode film containing either platinum or an alloy composed mainlyof platinum and containing at least either one of yttrium oxide andcerium oxide; and the step of firing the electrode film and thepiezoelectric/electrostrictive film adjacent to each othersimultaneously at a temperature of 1200° C. or higher. In thepiezoelectric/electrostrictive element, the electrode film contains 0.01to 0.60 part by weight of yttrium oxide to 100 parts by weight ofplatinum and contains 0.1 to less than 1.8 parts by weight of ceriumoxide to 1 part by weight of yttrium oxide. The electrode film aftersimultaneous firing has a thickness of 2.0 μm or less.

According to a third aspect of the invention, a laminatedpiezoelectric/electrostrictive element is manufactured by the followingsteps: the step of forming a piezoelectric/electrostrictive filmincluding a piezoelectric/electrostrictive material; the step of formingan electrode film containing either platinum or an alloy composed mainlyof platinum and containing yttrium oxide and cerium oxide, the electrodefilm containing 0.01 to 0.60 part by weight of yttrium oxide to 100parts by weight or platinum and containing 0.1 to less than 1.8 parts byweight of cerium oxide to 1 part by weight of yttrium oxide; and thestep of firing the electrode film and the piezoelectric/electrostrictivefilm adjacent to each other simultaneously at a temperature of 1200° C.or higher. In the piezoelectric/electrostrictive element, the electrodefilm after simultaneous firing has a thickness of 2.0 μm or less.

According to a fourth aspect of the invention, a laminatedpiezoelectric/electrostrictive element includes the follows: anelectrode film being a sintered body of either platinum or an alloycomposed mainly of platinum and having a thickness of 2.0 μm or less;and a piezoelectric/electrostrictive film being a sintered body of apiezoelectric/electrostrictive material containing 0.1 to 0.5 part byweight of calcium oxide to 100 parts by weight of platinum contained inthe electrode film and containing 0.2 to 3.0 parts by mol of ceriumoxide to 1 part by mol of calcium oxide.

According to a fifth aspect of the invention, a laminatedpiezoelectric/electrostrictive element is manufactured by the followingsteps: the step of forming a piezoelectric/electrostrictive filmincluding a piezoelectric/electrostrictive material; the step of formingan electrode film containing either platinum or an alloy composed mainlyof platinum and containing at least either one of calcium oxide andcerium oxide; and the step of firing the electrode film and thepiezoelectric/electrostrictive film adjacent to each othersimultaneously at a temperature of 1200° C. or higher. In thepiezoelectric/electrostrictive element, the electrode film contains 0.1to 0.5 part by weight of calcium oxide to 100 parts by weight ofplatinum and contains 0.2 to 3.0 parts by mol of cerium oxide to 1 partby mol of calcium oxide. The electrode film after simultaneous firinghas a thickness of 2.0 μm or less.

According to a sixth aspect of the invention, a laminatedpiezoelectric/electrostrictive element is manufactured by the followingsteps: the step of forming a piezoelectric/electrostrictive filmincluding a piezoelectric/electrostrictive material; the step of formingan electrode film containing either platinum or an alloy composed mainlyof platinum and containing calcium oxide and cerium oxide, the electrodefilm containing 0.1 to 0.5 part by weight off calcium oxide to 100 partsby weight of platinum and containing 0.2 to 3.0 parts by mol of ceriumoxide to 1 part by mol of calcium oxide; and the step of firing theelectrode film and the piezoelectric/electrostrictive film adjacent toeach other simultaneously at a temperature of 1200° C. or higher. In thepiezoelectric/electrostrictive element, the electrode film aftersimultaneous firing has a thickness of 2.0 μm or less.

It is therefore possible to simultaneously achieve a reduced thicknessand improved thermal resistance of the electrode film and a reducedchange in piezoelectric/electrostrictive properties with time. Thisproduces a piezoelectric/electrostrictive element with good initialpiezoelectric/electrostrictive properties and with a small change in thepiezoelectric/electrostrictive properties with time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a laminatedpiezoelectric/electrostrictive element according to a preferredembodiment of the invention.

FIG. 2 is a partially enlarged cross-sectional view of FIG. 1.

FIG. 3 provides a listing of the results of displacement measurements ontest samples 1 to 11 under different conditions, such as addition ornon-addition of yttrium oxide and cerium oxide, and the thickness of anelectrode film 73.

FIG. 4 provides a listing of the results of displacement measurements ontest samples 12 to 18 with different ways of adding yttrium oxide andcerium oxide and different thicknesses of the electrode film 73.

FIG. 5 provides a listing of the results of displacement measurements ontest samples 19 to 29 with different amounts of yttrium oxide and ceriumoxide added.

FIG. 6 provides a listing of the results of displacement measurements ontest samples 30 to 34 with different piezoelectric/electrostrictivematerials.

FIG. 7 provides a listing of the results of displacement measurements ontest samples 35 to 42 with different amounts of calcium oxide and ceriumoxide added.

DETAILED DESCRIPTION OF THE INVENTION

<Introduction>

According to the invention, in the manufacture of a laminatedpiezoelectric/electrostrictive element formed by lamination of apiezoelectric/electrostrictive film and an electrode film containingeither platinum or an alloy composed mainly of platinum and having athickness of 2.0 μm or less, both of yttrium oxide (Y₂O₃) or calciumoxide (CaO) (hereinafter referred to as a “first additive”) and ceriumoxide (CeO₂) (hereinafter referred to as a “second additive”) or eitherone of them is added to the electrode film or thepiezoelectric/electrostrictive film, and the electrode film and thepiezoelectric/electrostrictive film are fired simultaneously. Thissimultaneously achieves a reduced thickness and improved thermalresistance of the electrode film and a reduced change inpiezoelectric/electrostrictive properties with time, thereby producing apiezoelectric/electrostrictive element with good initialpiezoelectric/electrostrictive properties and with a small change in thepiezoelectric/electrostrictive properties with time.

<Example of Structure of Piezoelectric/electrostrictive Element>

FIGS. 1 and 2 show, by way of example, a structure of a laminatedpiezoelectric/electrostrictive element according to a preferredembodiment of the invention. FIG. 1 is a cross-sectional view of thepiezoelectric/electrostrictive element, and FIG. 2 is a partiallyenlarged cross-sectional view of FIG. 1. Thepiezoelectric/electrostrictive element whose structure is shown in FIGS.1 and 2 is a piezoelectric/electrostrictive actuator for use in a headof an inkjet printer, but the invention is also applicable to otherlaminated piezoelectric/electrostrictive elements than the one shown.

As shown in FIGS. 1 and 2, a piezoelectric/electrostrictive element 110is structured by laminating an electrode film 77, apiezoelectric/electrostrictive film 793 (79), an electrode film 73, apiezoelectric/electrostrictive film 795 (79), and an electrode film 75,in this order, on a diaphragm 66 that is an upper surface of a substrate44. In the piezoelectric/electrostrictive element 110, the applicationof a drive signal between the electrode films 77, 75 and the electrodefilm 73 induces a flexural displacement of a working part 78 that isformed by alternate laminations of the electrode films 77, 73, 75 andthe piezoelectric/electrostrictive films 793, 795. While FIGS. 1 and 2show the piezoelectric/electrostrictive element 110 of a total of fivelayers including three layers of the electrode films 77, 73, and 75 andtwo layers of the piezoelectric/electrostrictive films 793 and 795, itis possible to alter the number of layers of the electrode film and thepiezoelectric/electrostrictive film.

The substrate 44 is a sintered body of an insulating material. Theinsulating material may preferably be zirconium oxide (ZrO₂) withaddition of a stabilizer such as calcium oxide (CaO), magnesium oxide(MgO), yttrium oxide (Y₂O₃), ytterbium oxide (Yb₂O₃), or cerium oxide(Ce₂O₃). That is, it is preferable to adopt a stabilized zirconium oxideor a partially stabilized zirconium oxide.

The substrate 44 includes a cavity 46 and is structured to support thediaphragm 66 in the middle with a peripheral supporting part 68.Adopting this structure to support the diaphragm 66 having a small platethickness with the supporting part 68 having a large plate thicknessallows the substrate 44 to retain its mechanical strength even if thediaphragm 66 has a reduced plate thickness. This allows an increase inflexural displacement of the piezoelectric/electrostrictive element 110.

The piezoelectric/electrostrictive films 793 and 795 are sintered bodiesof a piezoelectric/electrostrictive material. Thepiezoelectric/electrostrictive material may preferably be a lead(Pb)-based perovskite compound. Of lead-based perovskite compounds, itis preferable to adopt a binary one of lead titanate (PbTiO₃) and leadzirconate (PbZrO₃); a ternary one of lead titanate, lead zirconate, anda third component; or either the binary or ternary one with addition ofa metal oxide. In particular, it is preferable to adopt a lead-basedperovskite compound formed by a ternary compound of lead titanate, leadzirconate, and lead magnesium-niobate oxide (Pb(Mg_(1/3)Nb_(2/3))O₃)with addition of a nickel oxide (NiO). Examples of the ternary compoundas a main component include a composite material made of lead titanatezirconate and one or more kinds of materials selected from a group ofPb(Mg_(1/3)Nb_(2/3))O₃, Pb(Ni_(1/3)Nb_(2/3))O₃, Pb(Zn_(1/2)Nb_(1/2))O₃,and Pb(Yb_(1/2)Nb_(1/2))O₃ and, in particular, having a tetragonalcrystal system at room temperature. The piezoelectric/electrostrictivefilms 793 and 795 may preferably be formed by firing after filmdeposition by screen printing. It is of course possible to adopt otherdeposition methods than screen printing.

The electrode film 77 may preferably be a sintered body of platinum (Pt)with addition of titanium oxide (TiO₂). Of course, it is possible toadopt other conductive materials than platinum with addition of atitanium oxide.

The electrode film 73 is a sintered body of either platinum or an alloycomposed mainly of platinum (hereinafter referred to as “platinumalloy”). The electrode film 73 may preferably have a thickness of 0.5 to2.0 μm. This is because the electrode film 73 with a thickness belowthis range tends to cause disconnection at the time of simultaneousfiring, and also because the electrode film 73 with a thickness abovethis range tends to deteriorate initial piezoelectric/electrostrictiveproperties.

Also, it is desirable that the electrode film 73 be made of a cermetmaterial consisting of a conductive material and apiezoelectric/electrostrictive material forming thepiezoelectric/electrostrictive films 793 and 795. The electrode film 73of such a material allows the speeds of shrinkage of thepiezoelectric/electrostrictive films 793, 795 and of the electrode film73 at the time of simultaneous firing to be brought closer to eachother.

The electrode film 75 may preferably be a sintered body of gold (Au). Ofcourse, conductive materials than gold may be adopted.

The electrode films 77, 73, and 75 may preferably be formed by tiringafter film deposition by screen printing. It is of course possible toadopt other deposition methods than screen printing.

The first additive (yttrium oxide or calcium oxide) can be added to thepiezoelectric/electrostrictive films 793, 795 or to the electrode film73 prior to simultaneous firing, and the second additive (cerium oxide)can be added to the piezoelectric/electrostrictive films 793, 795 or tothe electrode film 73 prior to simultaneous firing. It is to be notedthat at least either one of the first and second additives, and morepreferably both of the first and second additives, should be added tothe electrode film 73. This is because such addition can improve thethermal resistance of platinum alloys forming the electrode film 73 andcan reduce the thickness of the electrode film 73.

For addition of the first additive to the piezoelectric/electrostrictivefilms 793 and 795 prior to simultaneous firing, a first additive powderis added to a powder of the piezoelectric/electrostrictive materialdescribed above and may be used as it is or used after calcination. Foraddition of the first additive to the electrode film 73 prior tosimultaneous firing, a first additive powder is added to a powder of theplatinum alloy described above and used as it is.

Similarly, for addition of the second additive to thepiezoelectric/electrostrictive films 793 and 795 prior to simultaneousfiring, a second additive powder is added to the powder of thepiezoelectric/electrostrictive material described above and may be usedas it is or used after calcination. For addition of the second additiveto the electrode film 73 prior to simultaneous firing, a second additivepowder is added to a platinum alloy powder and used as it is.

In the case of adding both or either one of the first and secondadditives to the electrode film 73 prior to simultaneous firing, thepiezoelectric/electrostrictive films 793 and 795, before simultaneouslyfiring with its adjacent electrode film 73 at a temperature of 1200° C.or higher, contain substantially no additive, but after simultaneousfiring with the electrode film 73, they contain the additive(s). On theother hand, the electrode film 73 contains the additive(s) beforesimultaneously firing with the adjacent piezoelectric/electrostrictivefilms 793 and 795, but after simultaneous firing with thepiezoelectric/electrostrictive films 793 and 795, it containssubstantially no additive. Here, “containing substantially no additive”refers to the state that the piezoelectric/electrostrictive films 793,795 or the electrode film 73 is regarded as not containing the first orsecond additive even though they contain them in such a very smallamount as not to affect the properties of thepiezoelectric/electrostrictive films 793, 795 or the electrode film 73.

The first and second additives diffuse from the electrode film 73 to thepiezoelectric/electrostrictive film 79 at the time of simultaneousfiring of the electrode film 73 and the piezoelectric/electrostrictivefilms 793 and 795. This is because the first and second additives have alow degree of solid solubility in platinum but have a high degree ofsolid solubility in a lead-based perovskite compound. Such movement ofthe first and second additives is feasible by adding both or either oneof the first and second additives, in addition to adding either aplatinum powder or a powder of an alloy composed mainly of platinum, toan electrode paste for use in the formation of the electrode film 73.

In the case of selecting yttrium oxide as the first additive, a contentof yttrium oxide in the piezoelectric/electrostrictive film 79 aftersimultaneous firing may preferably be 0.01 to 0.60 part by weight, morepreferably 0.02 to 0.40 part by weight, to 100 parts by weight ofplatinum contained in the electrode film 73. This is because the contentbelow this range tends to deteriorate initialpiezoelectric/electrostrictive properties, and also because the contentabove this range tends to involve an increase in the amount of ceriumoxide added and to thereby deteriorate the initialpiezoelectric/electrostrictive properties.

Further, a content of cerium oxide in the electrode film 73 prior tosimultaneous firing, that is, a content of cerium oxide in thepiezoelectric/electrostrictive film 79 after simultaneous firing, maypreferably be 0.1 to less than 1.8 parts by weight to 1 part by weightof yttrium oxide. This is because the content below this range tends toincrease a change in the piezoelectric/electrostrictive properties withtime, and also because the content above this range tends to deteriorateinitial piezoelectric/electrostrictive properties.

In the case of selecting calcium oxide as the first additive, a contentof calcium oxide in the piezoelectric/electrostrictive film 79 aftersimultaneous firing may preferably be 0.1 to 0.5 part by weight to 100parts by weight of platinum contained in the electrode film 73. This isbecause the content below this range tends to deteriorate initialpiezoelectric/electrostrictive properties, and also because the contentabove this range tends to involve an increase in the amount of ceriumoxide added and thereby deteriorate the initialpiezoelectric/electrostrictive properties.

Further, a content of cerium oxide in the electrode film 73 prior tosimultaneous firing, that is, a content of cerium oxide in thepiezoelectric/electrostrictive film 79 after simultaneous firing, maypreferably be 0.2 to 3.0 parts by mol to 1 part by mol of calcium oxide.This is because the content below this range tends to increase a changein the piezoelectric/electrostrictive properties with time, and alsobecause the content above this range tends to deteriorate initialpiezoelectric/electrostrictive properties.

<Experiment>

The following description contains evaluation results of thepiezoelectric/electrostrictive element shown in FIGS. 1 and 2 underdifferent conditions, such as the amounts of the first and secondadditives added, the ways of adding the first and second additives, thethickness of the electrode film 73, and thepiezoelectric/electrostrictive material to be used. In the manufactureof the piezoelectric/electrostrictive element 110, the substrate 44 isfirst prepared. The substrate 44 is prepared by firing a ceramic greenlaminate formed by lamination of ceramic green sheets of partiallystabilized zirconium oxide, at a temperature of 1450° C.

Then, the working part 78 is formed on the diaphragm 66 of the substrate44.

In the formation of the working part 78, initially, a lower-electrodepaste containing a platinum powder and a titanium oxide powder isapplied onto the diaphragm 66 by screen printing, and the electrode film77 formed as a result is fired at 1300° C., This generates a sinteredbody of the electrode film 77 integrated with the substrate 44.

Subsequently, a piezoelectric/electrostrictive paste containing acalcined piezoelectric/electrostrictive material powder, aninner-electrode paste including a platinum powder, and apiezoelectric/electrostrictive paste are applied in sequence by screenprinting, and the piezoelectric/electrostrictive film 793, the electrodefilm 73, and the piezoelectric/electrostrictive film 795 that are formedas a result are simultaneously fired at 1250° C. This generates asintered body of the piezoelectric/electrostrictive film 793, theelectrode film 73, and the piezoelectric/electrostrictive film 795,integrated with the substrate 44 and the electrode film 77. Thepiezoelectric/electrostrictive material employed may be any one of thefollowing:

16Pb(Mg_(1/3)Nb_(2/3))O₃+4Pb(Ni_(1/3)Nb_(2/3))O₃+43PbTiO₃+37PbZrO₃(hereinafter referred to as a “piezoelectric/electrostrictive materialA”); 20Pb(Mg_(1/3)Nb_(2/3))O₃+43PbTiO₃+37PbZrO₃ (hereinafter referred toas a “piezoelectric/electrostrictive material B”);30Pb(Ni_(1/3)Nb_(2/3))O₃+42PbTiO₃+28PbZrO₃ (hereinafter referred to as a“piezoelectric/electrostrictive material C”);10Pb(Yb_(1/2)Nb_(1/2))O₃+48PbTiO₃+42PbZrO₃ (hereinafter referred to as a“piezoelectric/electrostrictive material D”); and24Pb(Zn_(1/2)Nb_(1/2))O₃+40PbTiO₃+36PbZrO₃ (hereinafter referred to as a“piezoelectric/electrostrictive material E”).

Still subsequently, an upper-electrode paste containing a gold powder isapplied by screen printing, and the electrode film 75 formed as a resultis fired at 800° C. This generates a sintered body of the electrode film75.

In the formation of the working part 78, a pattern of the electrode film77, the piezoelectric/electrostrictive film 793, the electrode film 73,the piezoelectric/electrostrictive film 795, and the electrode film 75is such that the electrode films 75 and 77 are electrically at the samepotential; the electrode films 77 and 73 face each other with thepiezoelectric/electrostrictive film 793 in between; and the electrodefilms 73 and 79 face each other with the piezoelectric/electrostrictivefilm 795 in between. Further, the thicknesses of the lower-electrodepaste, the inner-electrode paste, the upper-electrode paste, and thepiezoelectric/electrostrictive paste at the time of application arecontrolled so that the electrode film 77, thepiezoelectric/electrostrictive film 793, the electrode film 73, thepiezoelectric/electrostrictive film 795, and the electrode film 75 afterfiring have thicknesses or 2.0 μm, 7.5 μm, 1.1 to 2.0 μm (describedlater), 8.0 μm, and 0.2 μm, respectively.

In order for the electrode film 73 to contain the first and secondadditives prior to simultaneous firing, a platinum powder with additionof first and second additive powders is used as the inner-electrodepaste. This inner-electrode paste can be obtained by adding first andsecond additive powders of reagent grade to a platinum powder with acrystallite diameter of 60 nm to 100 nm and further adding a dispersant,a binder, and a solvent thereto, and kneading with a three roll mill. Atthis time, it is desirable that a content of the first additivepreviously contained in the platinum powder be quantitatively determinedby ICP (Inductively Coupled Plasma) or the like, and then inconsideration of this content, the first additive powder be added toachieve a desired amount of the first additive added.

Meanwhile, in order to allow the piezoelectric/electrostrictive film 79prior to simultaneous firing to contain the first and second additives,a piezoelectric/electrostrictive material powder with addition of firstand second additive powders is used as thepiezoelectric/electrostrictive paste. Thispiezoelectric/electrostrictive paste can be obtained by adding first andsecond additive powders of reagent grade to apiezoelectric/electrostrictive material powder that does notsubstantially contain a first or second additive, and after calcinationat 1000° C., further adding a dispersant, a binder, and a solventthereto, and kneading with a three roll mill.

After the formation of the working part 78, a voltage of 100 V isapplied between the electrode films 77, 75 and the electrode film 73 ata temperature of 100° C. for polarization of thepiezoelectric/electrostrictive element 110.

Then, an initial flexural displacement is measured immediately after thepolarization. Further, the piezoelectric/electrostrictive element 110 isleft at room temperature and room humidity without application ofvoltage in order to measure flexural displacements after one week, aftertwo weeks, and after three weeks, respectively. The “displacement” hererefers to a displacement measured with a laser Doppler displacement gagewhen a drive voltage of 30 V is applied between the electrode films 77,75 and the electrode film 73.

Still further, the thickness of the electrode film 73 in thepiezoelectric/electrostrictive element 110 is measured after themeasurement of the flexural displacement. This thickness is measured bypolishing the piezoelectric/electrostrictive element 110 thereby toexpose and observe the electrode film 73 with an electron microscope.

FIGS. 3 to 6 show the results of displacement measurements on testsamples 1 to 34 manufactured, selecting yttrium oxide as the firstadditive and under different conditions such as the amounts of yttriumoxide and cerium oxide added, the ways of adding yttrium oxide andcerium oxide, the thickness of the electrode film 73, and thepiezoelectric/electrostrictive material used. FIG. 7 shows the resultsof displacement measurements on test samples 35 to 42 manufactured,selecting calcium oxide as the first additive and under differentconditions such as the amounts of calcium oxide and cerium oxide, andthe thickness of the electrode film 73. In FIGS. 3 to 7, “(Part byWeight)” in the “Amount of Y₂O₃, CaO, or CeO₂ Added” column refers to apart by weight to 100 parts by weight of platinum contained in theelectrode film 73. Also, “(Molar Ratio)” in the “Amount of CeO₂ Added”column refers to a ratio of the amount of substance of cerium oxide tothe amount of substance of calcium oxide. The “Displacement” column inFIGS. 3 to 7 contains mean values of displacements calculated with 30 ormore piezoelectric/electrostrictive elements 110. Variations indisplacement measurements are approximately ±0.002 p.m. Further, the“Thickness” column in FIGS. 3 to 7 contains mean values calculated with10 or more piezoelectric/electrostrictive elements 110. Variations inthickness measurements are approximately ±0.1 μm.

Influence of Addition or Non-Addition of Yttrium Oxide and Cerium Oxide

FIG. 3 provides a listing of the results of displacement measurements onthe test samples 1 to 11 under different conditions such as addition ornon-addition of yttrium oxide and cerium oxide, and the thicknesses ofthe electrode film 73. Piezoelectric/electrostrictive material A is usedfor test samples 1 to 11b, and in the case of adding yttrium oxide, 0.1part by weight of yttrium oxide be added to the electrode film 73 priorto simultaneous firing, or in the case of adding cerium oxide, 0.6 partby weight of cerium oxide be added to the electrode film 73 prior tosimultaneous firing.

As shown in FIG. 3, referring to the test samples 1 to 3 with noaddition of yttrium oxide nor cerium oxide, the test sample 1 where theelectrode film 73 has a thickness of 2.5 μm shows an undesirable initialdisplacement of 0.165 μm. On the other hand, out of the test samples 1to 3, the test sample 2 where the electrode film 73 has a reducedthickness of 1.8 μm shows a good initial displacement of 0.190 μm, butshows an undesirable change of displacement with time, specifically−0.015 μm in three weeks. The test sample 3 where the electrode film 73has a reduced thickness of 1.6 μm suffers a disconnection of theelectrode film 73.

Referring now to the test samples 4 to 6 with addition of yttrium oxidebut no addition of cerium oxide, the test samples 4 and 5 where theelectrode films 73 have thicknesses of 1.9 μm and 1.4 μm, respectively,show good initial displacements of 0.199 μm and 0.216 μm, respectively,but show undesirable changes of displacement with time, specifically−0.017 μm and −0.016 μm, respectively, in three weeks. On the otherhand, the test sample 6 where the electrode film 73 has a reducedthickness of 1.3 μm suffers a disconnection of the electrode film 73.

Referring further to the test samples 7 to 9 with addition of ceriumoxide but no addition of yttrium oxide, the test samples 7 and 8 wherethe electrode films 73 have thicknesses of 1.8 μm and 1.6 μm,respectively, show good initial displacements of 0.192 μm and 0.210 μm,respectively, and also favorable changes of displacement with time,specifically both −0.002 μm three weeks. On the other hand, the testsample 9 where the electrode film 73 has a reduced thickness of 1.2 μmsuffers a disconnection of the electrode film 73.

On the other hand, referring to the test samples 10 and 11 with additionof both yttrium oxide and cerium oxide, the test samples 10 and 11 wherethe electrode films 73 have thicknesses of 1.8 μm and 1.2 μm,respectively, show good initial displacements of 0.200 μm and 0.228 μm,respectively, and also favorable changes of displacement with time,specifically −0.002 μm and −0.001 μm, respectively, in three weeks.Besides, even the test sample 11 where the electrode film 73 has areduced thickness of 1.2 μm suffers no disconnection of the electrodefilm 73.

From the results, it can be concluded that, in the case of adding bothyttrium oxide and cerium oxide, good initial displacements and favorablechanges of displacement with time can be achieved even if the thicknessof the electrode film 73 is 2.0 μm or less, and the thickness of theelectrode film 73 can be reduced to at least 1.2 μm.

Influence of Ways of Adding Yttrium Oxide and Cerium Oxide

FIG. 4 provides a listing of the results of displacement measurements onthe test samples 12 to 18 with different ways of adding yttrium oxideand cerium oxide and different thicknesses of the electrode film 73.Piezoelectric/electrostrictive material A is used for test samples 12 to18, and 0.1 part by weight of yttrium oxide and 0.6 part by weight ofcerium oxide be added to the electrode film 73 or to thepiezoelectric/electrostrictive film 9 prior to simultaneous firing.

As shown in FIG. 4, referring to the test samples 12 to 14 with additionof both yttrium oxide and cerium oxide to thepiezoelectric/electrostrictive film 79, the test sample 12 where theelectrode film 73 has a thickness of 1.8 μm shows a good initialdisplacement of 0.200 μm, and also a favorable change of displacementwith time, specifically −0.002 μm in three weeks. However, the testsamples 13 and 14 where the electrode films 73 have reduced thicknessesof 1.5 μm and 1.2 μm, respectively, suffer disconnections of theelectrode films 73.

Referring to the test samples 15 and 16 with addition of yttrium oxideto the electrode film 73 and cerium oxide to thepiezoelectric/electrostrictive film 79, the test sample 15 where theelectrode film 73 has a thickness of 1.4 μm shows a good initialdisplacement of 0.220 μm, and also a favorable change of displacementwith time, specifically −0.004 μm in three weeks. However, the testsample 16 where the electrode film 73 has a reduced thickness of 1.2 μmsuffers a disconnection of the electrode film 73.

Referring further to the test samples 17 and 18 with addition of yttriumoxide to the piezoelectric/electrostrictive film 79 and cerium oxide tothe electrode film 73, the test sample 17 where the electrode film 73has a thickness of 1.6 μm shows a good initial displacement of 0.216 μm,and desirably no change of displacement with time, ±0.000 μm in threeweeks. However, the test sample 18 where the electrode film 73 has areduced thickness of 1.2 μm suffers a disconnection of the electrodefilm 73.

From the results, it can be concluded that, in the case of adding bothor either one of yttrium oxide and cerium oxide to thepiezoelectric/electrostrictive film 79, as in the case of adding bothyttrium oxide and cerium oxide to the electrode film 73, good initialdisplacements and favorable changes of displacement with time can beachieved even if the thickness of the electrode film 73 is 2.0 μm orless; however, unlike in the case of adding both yttrium oxide andcerium oxide to the electrode film 73, the thickness of the electrodefilm 73 cannot be reduced to 1.2 μm.

Influence of Amounts of Yttrium Oxide and Cerium Oxide Added FIG. 5provides a listing of the results of displacement measurements on thetest samples 19 to 29 with different amounts of yttrium oxide and ceriumoxide added. Piezoelectric/electrostrictive material A is used for testsamples 19 to 29; yttrium oxide and cerium oxide be added to theelectrode film 73 prior to simultaneous firing; and the thickness of theelectrode film 73 be in the range of 1.1 to 1.3 μm.

As shown in FIG. 5, the test samples 19 to 22 and 24 to 28 with additionof 0.01 to 0.60 part by weight of yttrium oxide and addition of 0.1 toless than 1.8 parts by weight of cerium oxide show especially goodinitial displacements in the range of 0.220 to 0.230 μm. However, thetest sample 23 with addition of 1.8 parts by weight of cerium oxide, andthe test sample 29 with addition of more than 0.6 part by weight ofyttrium oxide tend to show reduced initial displacements of 0.212 μm and0.210 μm, respectively.

Influence of Piezoelectric/Electrostrictive Material

FIG. 6 provides a listing of the results of displacement measurements onthe test samples 30 to 34 with different piezoelectric/electrostrictivematerials. For the test samples 30 to 34, let 0.1 part by weight ofyttrium oxide and 0.6 part by weight of cerium oxide be added to theelectrode film 73 prior to simultaneous firing, and the thickness of theelectrode film 73 be in the range of 1.1 to 1.2 μm.

As shown in FIG. 6, the test samples 30 to 36 show good initialdisplacements of 0.195 to 0.230 μm and also favorable changes ofdisplacement with time, specifically in the range of −0.003 to +0.001 μmin three weeks.

This indicates that the effect of addition of yttrium oxide and ceriumoxide can be achieved irrespective of the piezoelectric/electrostrictivematerial.

Influence of Amounts of Calcium Oxide and Cerium Oxide Added

FIG. 7 provides a listing of the results of displacement measurements onthe test samples 35 to 42 with different amounts of calcium oxide andcerium oxide. Piezoelectric/electrostrictive material A is used for testsamples 35 to 42; calcium oxide and cerium oxide be added to theelectrode film 73 prior to simultaneous firing; and the thickness of theelectrode film 73 be in the range of 1.1 to 1.3 μm.

As shown in FIG. 7, the test samples 35 to 42 with addition of 0.1 to0.5 part by weight of calcium oxide and 0.2 to 3 molar ratio of ceriumoxide show good initial displacements of 0.225 to 0.231 μm, and alsofavorable changes of displacement with time, specifically in the rangeof −0.002 to +0.002 μm in three weeks.

<Verification of Movement of Yttrium Oxide, Calcium Oxide, and CeriumOxide>

The test samples 12 to 42 described above are subjected to ion etchingto expose their cross-sections, and the distribution of yttrium oxide,calcium oxide, and cerium oxide is investigated by electron probe microanalysis (EPMA). The result is that no segregation of cerium oxide,calcium oxide, and yttrium oxide is recognized in the vicinity of theelectrode film 73 nor in the piezoelectric/electrostrictive film 79.

Further, the test samples 12 to 42 described above are subjected to ionetching to expose their cross-sections, and only their working parts 78are dissolved to quantitatively determine the contents of yttrium oxide,calcium oxide, and cerium oxide in a resultant solution by ICP. Theresult is that equivalent amounts of yttrium oxide, calcium oxide, andcerium oxide contents to the amounts added are recognized.

Moreover, an inner-electrode paste obtained by adding a yttrium oxidepowder and a cerium oxide powder to a platinum powder is applied onto asubstrate of zirconium oxide by screen printing, and then, a resultantfilm is tired and observed. As a result, segregation of yttrium oxideand cerium oxide is recognized in the surface. This indicates thatyttrium oxide and cerium oxide have a low degree of solid solubility inplatinum contained in the inner-electrode paste. Also, aninner-electrode paste obtained by adding a calcium oxide powder and acerium oxide powder to a platinum powder is applied on a substrate ofzirconium oxide by screen printing, and then, a resultant film is firedand observed. The result is that segregation of calcium oxide and ceriumoxide is recognized in the surface. This indicates that calcium oxideand cerium oxide have a low degree of solid solubility in platinumcontained in the inner-electrode paste.

From the facts described above, it is conceivable that yttrium oxide,calcium oxide, and cerium oxide will diffuse from the electrode film 73to the piezoelectric/electrostrictive film 79 without evaporation at thetime of simultaneous firing, and they are distributed uniformly within asintered body of the piezoelectric/electrostrictive film 79 aftersimultaneous firing.

<Others>

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

What is claimed is:
 1. A laminated piezoelectric/electrostrictiveelement comprising: an electrode film being a sintered body of eitherplatinum or an alloy composed mainly of platinum and having a thicknessof 2.0 μm or less; and a piezoelectric/electrostrictive film, directlycontacting said electrode film and comprising a sintered body of apiezoelectric/electrostrictive material including 0.1 to 0.5 part byweight of calcium oxide to 100 parts by weight of platinum contained insaid electrode film and containing 0.2 to 3.0 parts by mol of ceriumoxide to 1 part by mol of calcium oxide.
 2. The laminatedpiezoelectric/electrostrictive element according to claim 1, whereinsaid piezoelectric/electrostrictive material is composed mainly of acomposite material including lead titanate zirconate and one or morematerials selected from the group consisting of Pb(Mg_(1/3)Nb_(2/3))O₃,Pb(Ni_(1/3)Nb_(2/3))O₃, Pb(Zn_(1/2)Nb_(1/2))O₃, andPb(Yb_(1/2)Nb_(1/2))O₃.
 3. The laminated piezoelectric/electrostrictiveelement according to claim 2, wherein saidpiezoelectric/electrostrictive material has a tetragonal crystal systemat room temperature.